- A
On both REs: request system software add <image>; then request system reboot both REs simultaneously.
Why wrong: Incorrect: Simultaneous reboot causes outage.
- B
On RE0: request system software add <image> re0; on RE1: request system software add <image> re1; then request system reboot both.
Why wrong: Incorrect: No switchover before reboot.
- C
On RE0 (primary): request system software add <image> re0; request system reboot re0. After reboot, on RE1: request system software add <image> re1; request system reboot re1.
Why wrong: Incorrect: Upgrading primary first causes traffic loss.
- D
On RE1 (backup): request system software add <image> re1; request system reboot re1. After reboot, request chassis routing-engine master switch. On RE0 (now backup): request system software add <image> re0; request system reboot re0.
Correct: Follows best practice for minimal disruption.
Quick Answer
The correct sequence is to upgrade and reboot the backup RE first, then perform a graceful mastership switch, and finally upgrade and reboot the former primary. This order is correct because it leverages Graceful Routing Engine Switchover (GRES) to maintain forwarding state and minimize traffic loss during the hitless RE upgrade. By rebooting the backup RE while the primary continues forwarding, then switching mastership so the newly upgraded RE takes over, the other RE can be upgraded without ever leaving the router without an active control plane. On the JNCIA-Junos exam, this question tests your understanding of the sequential reboot sequence required for a non-disruptive Junos upgrade, and a common trap is attempting to upgrade both REs simultaneously or rebooting the primary first. Remember the memory tip: “Backup first, switch, then the rest”—always upgrade the standby RE, make it master, then upgrade the former master.
JNCIA-JUNOS Operational Monitoring and Maintenance Practice Question
This JNCIA-JUNOS practice question tests your understanding of operational monitoring and maintenance. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
You are the network administrator for a large enterprise with a Juniper MX480 router running Junos 18.2R3. The router has two Routing Engines (RE0 and RE1) in a graceful Routing Engine switchover (GRES) configuration. During a scheduled maintenance window, you need to upgrade the Junos OS to a newer version while minimizing traffic loss. The upgrade process requires a reboot of both REs. You have staged the software on both REs. Which sequence of commands should you use to perform the upgrade with minimal disruption?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
On RE1 (backup): request system software add <image> re1; request system reboot re1. After reboot, request chassis routing-engine master switch. On RE0 (now backup): request system software add <image> re0; request system reboot re0.
Option D is correct because it performs a hitless upgrade by first upgrading and rebooting the backup RE (RE1), then performing a graceful mastership switch using 'request chassis routing-engine master switch', and finally upgrading and rebooting the former primary (now backup) RE0. This sequence ensures that during each RE reboot, the other RE remains active and continues forwarding traffic, leveraging GRES to maintain state and minimize packet loss.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
On both REs: request system software add <image>; then request system reboot both REs simultaneously.
Why it's wrong here
Incorrect: Simultaneous reboot causes outage.
- ✗
On RE0: request system software add <image> re0; on RE1: request system software add <image> re1; then request system reboot both.
Why it's wrong here
Incorrect: No switchover before reboot.
- ✗
On RE0 (primary): request system software add <image> re0; request system reboot re0. After reboot, on RE1: request system software add <image> re1; request system reboot re1.
Why it's wrong here
Incorrect: Upgrading primary first causes traffic loss.
- ✓
On RE1 (backup): request system software add <image> re1; request system reboot re1. After reboot, request chassis routing-engine master switch. On RE0 (now backup): request system software add <image> re0; request system reboot re0.
Why this is correct
Correct: Follows best practice for minimal disruption.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume 'request system reboot both' or rebooting the primary first is acceptable, not realizing that GRES requires a sequential upgrade with a manual mastership switch to avoid a full outage.
Detailed technical explanation
How to think about this question
GRES (Graceful Routing Engine Switchover) preserves interface and kernel state across RE failovers, but it requires that both REs run the same software version during the switchover. The upgrade process must therefore upgrade one RE at a time, ensuring the active RE is always running the new image before the other is rebooted. The 'request chassis routing-engine master switch' command triggers a controlled mastership transfer, allowing the backup to become primary without dropping adjacencies or forwarding state.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the JNCIA-JUNOS exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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Operational Monitoring and Maintenance — study guide chapter
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FAQ
Questions learners often ask
What does this JNCIA-JUNOS question test?
Operational Monitoring and Maintenance — This question tests Operational Monitoring and Maintenance — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: On RE1 (backup): request system software add <image> re1; request system reboot re1. After reboot, request chassis routing-engine master switch. On RE0 (now backup): request system software add <image> re0; request system reboot re0. — Option D is correct because it performs a hitless upgrade by first upgrading and rebooting the backup RE (RE1), then performing a graceful mastership switch using 'request chassis routing-engine master switch', and finally upgrading and rebooting the former primary (now backup) RE0. This sequence ensures that during each RE reboot, the other RE remains active and continues forwarding traffic, leveraging GRES to maintain state and minimize packet loss.
What should I do if I get this JNCIA-JUNOS question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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Last reviewed: Jun 11, 2026
This JNCIA-JUNOS practice question is part of Courseiva's free Juniper Networks certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the JNCIA-JUNOS exam.
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